1. Field of the Invention
The present invention generally relates to an oil activated fuel injector. More particularly, the present invention relates to a digital control valve used with an oil activated, electronically or mechanically controlled fuel injector.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically, or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two-, three-, or four-way valve systems, each having grooves or orifices that allow fluid communication between working ports, high pressure ports, and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid that is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as xe2x80x9cgroovesxe2x80x9d) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
However, in such a conventional system, a response time between the injection cycles may be slow, thus decreasing the efficiency of the fuel injector. This is mainly due to the slow movement of the control valve spool. More specifically, the slow movement of the control valve may result in a slow activation response time to begin the injection cycle. To remedy this inadequacy, additional pressurized working fluid may be needed; however, additional energy from the high pressure oil pump must be expended in order to provide this additional working fluid. This leads to an inefficiency in the operations of the fuel injector itself. Also, the working fluid at an end of an injection cycle may not be vented at an adequate response rate due to the slow movement of the control valve spool.
Other prior art systems use a small step at the end of the spool to reduce the area where the spool and the solenoid are in contact. However, these steps introduce wear due to impact between parts and reduced magnetic force between the spool and the solenoids.
According to a first aspect of the invention, a control valve for a fuel injector generally includes a valve body and a spool positioned within a bore of said valve body. The spool is slideable between a first and second position. The control valve also comprises a first bore in fluid communication with a rail inlet of the fuel injector, a cross bore positioned within the valve body and offset from the first bore, and a groove located about the spool. The cross bore, in embodiments, leads to ambient, and the first bore may be located within the valve body. The groove provides fluid communication between the cross bore and the first bore when the spool is in the first position, and seals fluid communication when the spool is in the second position. At least two solenoids are provided on opposing sides of the spool for moving the spool between the first and second positions, and a non-magnetic barrier is provided for controlling latching forces between the spool and at least one of the at least two solenoids when the spool is in the first position or the second position. The latching forces are created by a current pulse of one of the at least two solenoids. In embodiments, the solenoids are provided in end caps. The non-magnetic barrier may be a non-magnetic shim or a non-magnetic coating, and is preferably selected based upon the required or developed latching forces between the spool and the solenoids.